Method of making a mold for bidirectional hydrodynamic shaft seals

ABSTRACT

A method of making a mold for bidirectional hydrodynamic shaft seals wherein the mold face for forming the air side wall of the seal includes a plurality of circumferentially spaced, wedgeshaped recesses formed by a grinding wheel. The recesses are inclined with respect to the mold face and establish projecting cylindrical pads on the molded seal, the side walls of which have arcuate shapes and define triangular, grooved areas therebetween. The bases of the side walls operatively engage the shaft to be sealed in a trapezoidal contact pattern so as to be alternately effective to unidirectionally return leaking fluid upon a reversal of shaft rotation.

United States Patent 1 3,656,227 Weinand [451 1 Apr. 18, 1972 [54]METHOD OF MAKING A MOLD FOR 3,246,369 4/1966 Rhoads m1. ..1s/mc. 41BIDIRECTIONAL HYDRODYNAMIC 3,276,114 l0/l966 Blaurock ..29/527.l SHAFTSEALS 3,536,806 10/1970 Jackson ...18/DIG. 47

[72] Inventor: Louis ll. Weinand, Warren, Mich.

[73] Assignee: General Motors Corporation, Detroit,

Mich.

[22] Filed: Mar. 26, 1970 [21] Appl.No.: 22,978

[52] U.S.Cl. ..29/530,18/DlG.47 [51'] lnt.Cl..; ..B23p 17/00 [58]FieldofSearch ..29/527.l,530;18/DIG.47; 277/134 [56] References CitedUNITED STATES PATENTS 3,276,115 10/1966 Hansz ..29/527.1 3,497,2252/1970 Workman ..277/l34 Primary Examiner-J. Spencer OverholserAssistant Examiner-John E. Roethel Attorney-J. L. Carpenter, E. J Biskupand P. D. Sachtjen [57 ABSTRACT A method of making a mold forbidirectional hydrodynamic shaft seals wherein the mold face for formingthe air side wall of the seal includes a plurality of circumferentiallyspaced, wedge-shaped recesses formed by a grinding wheel. The recessesare inclined with respect to the mold face and establish projectingcylindrical pads on the molded seal, the side walls of which havearcuate shapes and define triangular, grooved areas therebetween. Thebases of the side walls operatively engage the shaft to be sealed in atrapezoidal contact pattern so as to be alternately effective tounidirectionally return leaking fluid upon a reversal of shaft rotation.

1 Claims, 7 Drawing Figures PATENTEDAPR 18 I972 3,656,227

ELL-N125 329] 7 BY 02115 [dema d flay/4.44%

ATTORNEY METHOD OF MAKING A MOLD FOR BIDIRECTIONAL IIYDRODYNAMIC SHAFISEALS Recently, hydrodynamic seals have become available for positivelysealing bidirectionally rotatable shafts. These bidirectional seals areof the type disclosed in my pending application, Ser. No. 577,236, filedon Sept. 6, 1966, now US. Pat. No. 3,515,395, and assigned to theassignee of the present invention wherein a surface on the air side ofthe seal is provided with a circumferentially alternating series oftriangular pads and grooves. The pads project radially inwardly from theair side surface and establish pairs of converging walled surfaces. lnassembly, the bases of the pads establish a series of wedge-shaped ortrapezoidal patterns with the shaft. Fluid leaking past the lip of theseal is carried within the groove into contact with one of the walledsurfaces which then functions as a hydrodynamic pump to displace thefluid across the lip to the reservoir. For the opposite direction ofshaft rotation, the other walled surface is effective to return theleaking fluid.

Bidirectional hydrodynamic shaft seals of the aforementioned type havegenerally required specialized tooling and manufacturing techniques toform the portion of the mold which establishes bidirectional walledsurfaces. Currently, numerous approaches have evolved for forming thealternating series of pads and grooves. In one method, an enlargedgroove pattern is made and, by a follower cam operated milling wheel,the pattern is transferred to an engraved on the mold member used forforming the air side wall. In another method, an electro-chemicalmachining process is used to transfer the bidirectional contact patternfrom a female pattern to the mold member to establish the desired seriesof pads and grooves. A further process utilizes photographic etching toform the pattern on the mold member. Those skilled in the art willappreciate that all of these processes require intermediate patterns andmanufacturing steps, sophisticated tooling techniques, and expensive andcomplex machining. As such, each mold takes considerable time and effortto produce mold parts which will repetitively produce the requiredcontact pattern on the mold element. In seals of this type which in manyinstances are specially designed for a particular application andenvironment, the cost attributable to these tooling operationsconstitutes a significant part of the article cost.

The present invention improves upon the above-mentioned techniques forthe manufacture of bidirectional seals by providing a method for makingbidirectional shaft seals in a considerably simplified manner.Generally, this method takes the form of directly grinding the moldmember for the air side wall of the seal to form a plurality ofcylindrical grooves which are mutually separated by triangular pads. Thearcuate side walls between the grooves and pads terminate adjacent theedge of the mold member which forms the seal lip. Preferably, thegrooves are formed by passing a grinding wheel across the conical faceof the mold member at a shallow approach angle with respect to the axisof the seal. In the mold cavity, these grooves constitute cylindricalrecesses into which the mold elastomer flows thereby forming, uponsolidification, a circumferential inwardly projecting series of pads.Thus, each pad is in the form of a wedge-shaped, cylindrical segmenthaving an axis lying in the same plane as the axis of the molded seal.In assembly, the bases of the arcuate side walls of the pads establish atrapezoidal contact pattern which is effective to unidirectionally pumpleaking fluid in the manner described above.

Accordingly, an object of the present invention is to provide asimplified method for forming a bidirectional contact pattern onhydrodynamic seals.

Another object of the present invention is to provide a method formaking a mold cavity for bidirectional hydrodynamic seals wherein acircumferential series of wedge-shaped recesses are formed by a grindingwheel in a mold face of the seal mold, the recesses forming a pluralityof cylindrical pads on the molded article which project therefrom andengage a surface to be sealed in a trapezoidal contact pattern and arealternately effective to unidirectionally pump leaking fluid upon areversal of shaft rotation.

A further object of the present invention is to provide a method ofmaking molded bidirectional hydrodynamic shaft seals by forming the airside mold face of the seal cavity with a plurality of ground recesseswhich establish on the molded seal a plurality of wedge-shaped,cylindrical segments having end portions adapted to contact the shaft ina trapezoidal contact pattern so as to be effective to unidirectionallyreturn fluid leaking past the seal lip regardless of the direction ofshaft rotation.

These and other objects will be apparent to one skilled in the art uponreading the following detailed description, reference being made to theaccompanying drawings in which:

FIG. 1 is a radially sectioned view of a seal mold for makingbidirectional hydrodynamic shaft seals in accordance with the presentinvention;

FIG. 2 is an enlarged view showing the grinding of the air side moldinsert to form a bidirectional molding pattern;

FIG. 3 is a view taken along line 3--3 of FIG. 2;

FIG. 4 is a side cross sectional view of a seal installationincorporating a shaft seal, made in accordance with the presentinvention;

FIG. 5 is a cross sectional view of the bidirectional hydrodynamic shaftseal shown in FIG. 4;

FIG. 6 is a view taken along line 6--6 of FIG. 5; and

FIG. 7 is an enlarged view of the bidirectional contact pattern betweenthe seal and the shaft.

Referring to the drawings, a seal mold 10 for making a bidirectionalhydrodynamic seal 12 comprises a lower mold element 14 and an upper moldelement 16 which are relatively axially separable. The lower moldelement 14 includes a base 18, an air side insert 20, and a cap member22. The upper mold element 16 includes a fluid sidle insert 24 and asleeve element 26. The seal mold 10 is generally conventional inconstruction and operation, the unit differing basically in the meansfor establishing the bidirectional sealing capabilities in the seal 12.In assembly, the above-mentioned elements establish an interior moldcavity conforming in shape to the molded portion of the seal 12.

The base 18 includes annular radial. flange 30, a conical face 32, and acircular base 34. The air side insert 20 is in the form of a truncatedcone and includes a conical surface 36, a base 38 engaging andcoextensive with the base 34, and a circular face 40. The cap member 22has a bottom surface 42 engaging the face 40 and radially outwardlydiverging conical surface 44. The conical surfaces 36 and 44 intersectto form an annular vertex 45.

The fluid side insert 24 includes a conical wall 46 and an axial face48. The sleeve element 26 includes a cylindrical surface 50 having aradially inwardly projecting annular rib 52 formed thereon. A V-shapedchannel 54 is formed between the parting surfaces 56 and 58 of the capmember 22 and the fluid side insert 24, respectively.

Preparatory to the molding of the elastomeric portion of the seal, ametallic seal casing 60, generally L-shaped in cross section, ispositioned in the seal mold 10 with a radial flange 62 thereof clampedbetween the flange 30 and the sleeve element 26 and extending into themold cavity. Thus, the casing 60 and ,the mold faces 50, 52, 48, 46, 44,36, and 32 establish the mold surfaces for forming the elastomericportion of the seal. By conventional molding techniques, the mold cavityis filled with a suitable elastomer to form a sealing annulus 70 whichis integrally bonded at the rim of the flange 62 to form thebidirectional hydrodynamic seal 12. The excess elastomer or flash in thechannel 54 is removed in a subsequent trimming operation.

More specifically, the conical surface or mold face 36 of the air sideinsert 20 is formed with a circumferentially alternating series ofrecesses and lands 82, the latter being, in effect, a continuation ofthe conical surface 36. The recesses 80, as shown in FIGS. 2 and 3, areformed by passing cylindrical grinding wheel 84 across the surface 36.More particularly, the air side insert 20 is mounted on. a shaft 86 forrotation about an axis 88. The grinding wheel 84 is mounted on a shaft90 for rotation about an axis 92. The axis 92 lies in a common planewith the axis 88 and, as illustrated, converges toward the latter at ashallow angle A which is less than conical angle B between the surface36 and the axis 88. Preferably, the angle A is less than 5 and may, ifdesirable, be parallel to or reversely inclined with respect to the axis88. The angle B generally should be greater than To form arepresentative recess 80, the cylindrical surface 85 of the grindingwheel 84 is passed across the surface 36 to a predetermined depth atwhich the tip of the recess 80 intersects the front face 40. For eachsubsequent recess 80, the air side insert is circumferentially indexedand the above grinding process repeated until the desired number ofrecesses 80 are formed about the circumference of the surface 36. Therecess 80, thus formed, will include a wedge-shaped, cylindrical face100 bounded by arcuate walls 102, adjacent pairs of which establishgenerally triangular tips 104.

Referring to FIGS. 4 through 7, a bidirectional hydrodynamic seal 12,made in accordance with the abovedescribed method, comprises theelastomeric sealing annulus 70 including a spring groove 110 formed bythe rib 52, an air side wall 112, and a fluid side wall 114 formed byconverging frustoconical surfaces. The air side wall 112 and the fluidside wall 114 intersect at a radially inwardly facing circumferentialseal lip 116 formed by the vertex 45. A helically coiled garter spring118 is retained in the groove 110 for radially inwardly biasing thesealing annulus 70. The spring 118 is located to the right of the seallip 116 so as to exert a maximum lip pressure to the right or air sideof the latter.

The above bidirectional hydrodynamic seal 12 also includes a pluralityof radially inwardly projecting pads 120 evenly circumferentially aboutthe air side wall 112 which corresponds to the recesses 80. The pads 120are mutually separated by grooves 122 corresponding to the lands 82.Each pad 120 is in the form of a cylindrical segment, as defined by acylindrical face 124 bounded by converging arcuate walled surfaces 125and 126 at the intersection with the grooves 122. The pads 120 have agradually increasing height in a direction away from the seal lip 116and an angle of convergence with respect to the seal axis which isshallower or less than the angle of the wall 112. The relieved areabetween adjacent walled surfaces 125 and 126 constitutes a continuationof the wall 112 and defines the generally triangular or V-shaped form ofgrooves 122.

As shown in FIG. 4, the casing 60 is mounted in a bore 130 of a housing132 with the pads and the seal lip 116 engaging the outer cylindricalsurface 136 of the shaft 138. The bases of the pads contact surface 136with the walled surfaces and 126 and form a generally trapezoidalcontact pattern 140, FIG. 7. The seal lip 116 establishes a continuouscircumferential contact with the surface 136. The fluid reservoir 142 isto the left of the static sealing surface 144 established between theseal lip 116 and the surface 136. As the shaft rotates in one directionfluid particle a, which has leaked past the surface 144, is carriedalong the shaft surface within the grooves 122 until it impinges againstthe walled surface 126. The inclination of the surface 126 causes fluidto be pumped past the surface 144 to the reservoir 142. For the oppositedirection of a shaft rotation, a fluid particle b impinges againstwalled surface 125 and is pumped from right to left past the sealingsurface 144 to the reservoir 142.

Although only one form of this invention has been shown and described,other forms will be readily apparent to those skilled in the art.Therefore, it is not intended to limit the scope of this invention bythe embodiment selected for the purpose of this disclosure, but only bythe claims which follow.

What is claimed is:

1. A method of making a seal mold for bidirectional hydrodynamic shaftseals, comprising the steps of: forming an annular cavity in said sealmold having radially inwardly converging frustoconical wallsintersecting at an annular vertex; and grinding a uniform series ofevenly circumferentially spaced concave cylindrical recessestangentially in one of said frustoconical walls at an arzgle ofinclination less than the co nical angle of said wall, sal recesseshaving axes intersecting the axis of said annular cavity and beingdefined by converging arcuate sides, said recesses being formed to adepth such that said arcuate sides converge and intersect at saidannular vertex with adjacent recesses being mutually separated byconical lands formed by said one of said frustoconical walls whereby themolded shaft seal is formed with a plurality of circumferentiallyspaced, wedge-shaped convex pads defined by cylindrical facescorresponding to said recesses bounded by arcuate walled surfacescorresponding to said arcuate sides and separated by conical groovescorresponding to said lands, the portions of said arcuate walledsurfaces adjacent said vertex being adapted to engage the shaft in atrapezoidal contact pattern such that the opposite walled surfaces arealternately effective to unidirectionally pump leaking fluid upon areversal of shaft rotation.

1. A method of making a seal mold for bidirectional hydrodynamic shaftseals, comprising the steps of: forming an annular cavity in said sealmold having radially inwardly converging frustoconical wallsintersecting at an annular vertex; and grinding a uniform series ofevenly circumferentially spaced concave cylindrical recessestangentially in one of said frustoconical walls at an angle ofinclination less than the conical angle of said wall, said recesseshaving axes intersecting the axis of said annular cavity and beingdefined by converging arcuate sides, said recesses being formed to adepth such that said arcuate sides converge and intersect at saidannular vertex with adjacent recesses being mutually separated byconical lands formed by said one of said frustoconical walls whereby themolded shaft seal is formed with a plurality of circumferentiallyspaced, wedge-shaped convex pads defined by cylindrical facescorresponding to said recesses bounded by arcuate walled surfacescorresponding to said arcuate sides and separated by conical groovescorresponding to said lands, the portions of said arcuate walledsurfaces adjacent said vertex being adapted to engage the shaft in atrapezoidal contact pattern such that the opposite walled surfaces arealternately effective to unidirectionally pump leaking fluid upon areversal of shaft rotation.